I have used fluorocarbon material for many years. My first experiences were not entirely satisfactory and didn't encourage me to abandon nylon, especially some of the newer nylon and copolymer type materials which are very good. I was introduced to Seaguar fluorocarbon by Tony Fordham of Fordham & Wakefield and after a while of using it my opinion changed and these monofilaments have become my first choice materials for most tasks.
Seaguar is amazingly tough, it is a little stiffer than most monofilament materials and of course like all fluorocarbons it has higher density which means that it sinks faster. These qualities make it perfect for fishing with large and heavy flies in salt and freshwater. I found Seaguar particularly good for use with tube flies for salmon and with large flies whilst coastal fishing for bass and pollack. In lighter sizes I first imagined that it may not allow enough movement of the fly but but I have used it very successfully for a long time despite that reservation.
Then Grand Max Soft-Plus became available. At long last I found the ideal leader material for virtually all of my fishing. It is more supple than most fluorocarbons and is reassuringly strong. I don’t consider breaking strain of leaders too important instead I match the leader to fly size to achieve mobility whilst the fly is fishing and to achieve good turnover. It’s almost ideal refractive index makes Soft-Plus practically invisible in water and allows me to use a stronger leader than most anglers might. In the lowest of low water, the smallest of rivers and with tiny flies I may use 3X, the same diameter that I would use for a cast of trout flies size 10 or for sea trout in a loch which is light enough by far to land a fish with confidence. For those who like to refer to breaking strain 3X Soft-Plus weighs in at 10.4lbs. If I increased my fly size I would automatically increase the leader size and in a biggish water 0.33mm (-1X) I would happily use with flies down to size 8 hooks. This has a BS close to 20lbs which is perfectly fine if you hook a monster and it allows smaller fish to be quickly brought to the bank.
Seaguar is still my choice for fly fishing in salt water and for making heavy leader butt and taper sections which cut beautifully into the wind but Grand Max Soft-Plus is the best all round leader and tippet material that I have so far encountered. Like all monofilament materials carefully tying and testing knots is essential and it is always good practice to examine leaders should you have any cause to think that they may have been damaged or inadvertently knotted.
After landing strong fish it is always a good idea to check knots and the fly attachment.